Would you mind to please elaborate on the hardware differences you can see.
Unfortunately, you are correct, there do not seem to be schematics readily available for newer revisions.
I have worked on V1.3 boards and have been used to having to power cycle occasionally, this might likely be tied to the current development, mainline, edge(here), and the fact that all is WIP.
I did look into the power cycling more thoroughly, and although there are a few 'net crumbs' to be found, nothing indicative that I have yet seen or tried.
At the moment I've had stable power on's with latest minimal build. Some of the work I've done in isolation has also improved boots.
Right now am testing cpu-frequency-scaling, I will add that v1 to main 6.1.11 fairly shortly its ready, I am adding proper current sensing to my test bench, for more elaborate stability testing, hopefully resulting in better v2
Next will most likely follow the progress with DRAM. I also prefer to work with debian os so not entirely sure if ubuntu has some difference.
While this doesn't answer your questions, these are known problems, and do not have definitive solutions anywhere right now.
